ULwimi oluCwangcisiweyo lweeNgxelo luLuhlu lweNgcaciso LwaseNtshonalanga
ULwimi oluCwangcisiweyo lweeNgxelo (SQL) ulwimi lolwazi. Zonke izigcawu zolwazi zanamuhla, ezibandakanya ukuFinyelela, iFayileMaker Pro, iMicrosoft SQL Server kunye ne-Oracle isebenzisa iSQL njengesiseko sayo sokwakha. Enyanisweni, ngokuqhelekileyo yindlela efanelekileyo yokuba usebenze kunye nedata ngokwalo. Zonke iifayile zokusebenzisa umzobo ezibonelela ngokungena kwedatha kunye nokusebenza kakubi akukho nto ngaphandle kwabaguquleli be-SQL. Bathatha izenzo ozenzayo ngokucacileyo kwaye uziguqulele kwiimigaqo ze-SQL eziqondwa yiziko ledatha.
I-SQL ifana nesiNgesi
Kule ngongoma, unokucinga ukuba awukho umprofeti kwaye ukufunda ulwimi lweprogram ngokuqinisekileyo aluyi kuphakamisa i-alley yakho. Ngethamsanqa, kwi-core yayo, i-SQL yilwimi elula. Inomlinganiselo omncinane wemiyalelo, kwaye loo mithetho iyafundwa kwaye iyalungiswa ngokufana nezivakalisi zesiNgesi.
Ukwazisa iiNgcaciso
Ukuqonda i-SQL, kubalulekile ukuba ube nolwazi oluyisiseko malunga nendlela yolwazi olusebenza ngayo. Ukuba ukhululekile ngamagama afana ne "tafile," "ulwalamano," kunye "nombuzo," zikhululeke ukulima phambili! Ukuba akunjalo, unokufisa ukufunda iinqununu ze- Database Database ngaphambi kokuba uqhubeke.
Makhe sibone umzekelo. Masithi unedatha elula ejoliswe ukugcina i-inventory yesitolo esilula. Enye yeetafile kwiziko lakho leenkcukacha zingabandakanya ixabiso lezinto kwieshelufu zakho ezikhokhelwe ngamanani eempahla ezikhethekileyo ezichonga into nganye. Unokwenza ukuba letafile ifake igama elilula njenge "Amaxabiso."
Mhlawumbi ufuna ukususa izinto ezisuka kwivenkile yakho exabiso elingaphezulu kwama-$ 25, uza "ukubuza" isiseko sedatha yazo zonke ezi zinto. Yilapho i-SQL ingena khona.
Umbuzo wakho wokuqala weSQL
Ngaphambi kokuba singene kwisitatimende se-SQL esifanele siphumelele le ngcaciso, makhe sizame ukuphinda umbuzo wethu kwisiNgesi. Sifuna "ukhethe zonke iinombolo zesitokhwe ukusuka kumaxabiso etafile apho ixabiso lingaphezu kwama-25 e-$." Yisicelo esihle kakhulu xa sichazwa kwisiNgesi esilula, kwaye sino-SQL elula. Nantsi inqaku elifanayo leSQL:
UKUHLOLA I-StockNumber
KWIIMALI
LAPHO Ixabiso> 5
Kulula nje oko! Ukuba ufunda le nkcazo ngasentla, uya kufumana ukuba iyafana kakhulu nombuzo wesiNgesi esikuyo kumhlathi wokugqibela.
Ukutolika amaStell Statements
Ngoku sizame omnye umzekelo. Eli xesha, nangona kunjalo, siya kuyenza emva. Okokuqala, ndiya kukunika isitatimende se-SQL kwaye makhe sibone ukuba unokuyichaza ngokucacileyo ngesiNgesi:
HLOLA Ixabiso
KWIIMALI
LAPHO I-StockNumber = 3006
Ngoko, ucinga ukuba le ntetho yenza ntoni? Eqinisile, ibuyisela intengo esuka kwisiseko sedatha ye-3006.
Kukhona isifundo esisodwa esilula kufuneka usikhuphe kwingxoxo yethu kule ngongoma: I-SQL ifana nesiNgesi. Musa ukukhathazeka malunga nendlela owakhiwa ngayo izitatimende ze-SQL; siya kufikelela kulo lonke uluhlu lwethu. Qaphela nje ukuba i-SQL ayisongelo njengoko ingaqala ukuvela.
Ubume beStell Statements
I-SQL inikeza uluhlu olubanzi lweengxelo, olukhethiweyo olulodwa. Nantsi imimiselo yezinye izitatimende eziqhelekileyo zeSQL:
- I-SQL INSERT ne-SQL DELETE: Ukufaka okanye ukususa irekhodi etafileni
- I-SQL NGAPHAMBILI: Iguqula iirekhodi kwitheyibhile
- I-SQL YADALA kunye ne-SQL DROP: Yakha okanye isuse itafile
Ukongeza kwezi nkcazo ze-SQL, ungasebenzisa izigatshana ze-SQL, phakathi kwazo ISAHLUKO siphila esetyenziswa kwimibandela yangaphambili. Ezi ziqendu zenza ulungise uhlobo lwedatha ukuze lusebenze. Ukongezwa kwinqatshana le-WHERE, nakhu amanye amacandelwana asetyenziswa ngokuqhelekileyo:
- KANYE OKANYE: OKUQINISELAYO: Hlanganisa iimeko ezininzi ukucoca isitatimende se-SQL
- NJENGE: Uthelekisa ixabiso kwiimpawu ezifanayo usebenzisa i-wildcard
- UKHENZISWA ngu: Ukuthumela idatha ekukhuphukeni okanye ekuhlaleni
Ukuba unomdla wokuqhubeka uhlola i-SQL, i- SQL Fundamentals yi-tutorial-part tutorial ephonononga izicwangciso kunye nemiba ye-SQL ngokubanzi.